Materials such as metal, ceramics and carbon exhibit a peculiar characteristic which is not observed in a bulk state by reducing the particle diameter (Y. Wang, N. Herron, J. Phys. Chem., 1991, 95, 525). Moreover, experiments and theoretical predictions have reported that in many cases, the peculiar characteristic appears in single nano-meter size and maximizes in sub-nano meter size range (L. Brus, J. Phys. Chem., 1986, 90, 2555).
For example, metal sub-nano particles have been known that their metallic characteristics disappear and form a discrete band structure by reducing the particle size (J. N. Solanki, Z. V. P. Murthy, Colloids and Surfaces A: Physicochem. Eng. Aspects, 2010, 359, 31). This characteristic has been examined to be applied to a pigment sensitizing solar cell or the like in the next generation for this reason because a light absorption derived from the band structure exhibits a characteristic like a semiconductor or a pigment molecule (A. Kogo, N. Sakai, T. Tatsuma, Electrochemistry Communications, 2010, 12, 996). Since it shows peculiar phenomena such as light emission and magnetization, which is not observed in a bulk state, it is expected to apply to various fields (X. Liu, M. Bauer, H. Bertagnolli, E. Roduner, J. V. Slageren, F. Phillip, Phys. Rev. Lett., 2006, 97, 253401).
In the case of semiconductor ceramic materials such as metal oxides and sulfides, the band gap energy greatly increases by forming the material into sub-nano particles by quantum size effect (Y. Wang, N. Herron, J. Phys. Chem., 1991, 95, 525 and L. Brus, J. Phys. Chem., 1986, 90, 2555). The variable band gap energy is useful in the photo-catalyst field or the like, and has expected to drastically improve catalyst activities and reaction selectivity and to produce a reaction that has not been shown in a bulk state.
Recently nano carbon materials have been noticed. Carbon material also obtains peculiar characteristics by forming into sub-nano particles. Particularly, since phenomenon such as white-color light emission under irradiation by an ultraviolet ray and up-conversion light emission are never produced in a bulk carbon, currently it has been researched (J. Zong, Y. Zhu, X. Yang, J. Shen, C. Li, Chem. Commun., 2011, 47, 764).
The Non-Patent Documents such as S. L. Hu, K. Y. Niu, J. Sun, J. Yang, N. Q. Zhao and X. W. Du, J. Mater. Chem., 2009, 19, 484; Y. Negishi, K. Nobusada, T. Tsukuda, J. AM. CHEM. SOC., 2005, 127, 5261; N. Satoh, T. Nakashima, K. Kamikura, K. Yamamoto, Nature Nanotech., 2008, 3, 106; G. A. Ozin, S. Ozkar, R. A. Prokopowicz, Acc. Chem. Res., 1992, 25, 553; D. Tanaka, Y. Oaki, H. Imai, Chem. Commun., 2010, 46, 5286; and J. S. Beck, J. C. Vartuli, G. J. Kennedy, C. T. Kresge, W. J. Roth, S. E. Schramm, Chem. Mater., 1994, 6, 1816 have disclosed syntheses of minute particles such as metal which will be described later.